a. Field of the Invention
The present invention relates to a method of working steel machine parts including machining during quench cooling, and more particularly it relates to a composite tequnique consisting of machining and heat-treatment.
B. Description of the Prior Art
In general, the cutting of quench hardened steel machine parts is very difficult because of their high hardness. In some cases, turning of steel machine parts is performed by using cemented carbide cutting tools or ceramic tools, but the very low machinability of the parts results in the generation of heat, which, undesirably, often changes part of the steel structure. As a measure for avoiding this adverse effect, grinding, electrolytic working or spark-pressure working is employed. However, these working processes are low in working quality and requre a long period of time for a given working operation with a fixed amount to be cut, thus being inefficient. In order to increase productivity, the usual method adopted by manufacturers, though a roundabout way, is to effect cutting, such as turning, prior to quenching, and then effect quench hardening, which is followed by working such as grinding.
On the other hand, when the quenching process of steel is considered, it is seen that, as shown in FIGS. 1 and 2, it is within a relatively low-temperature region below the Ms point that quench hardening commences. In a higher-temperature region, the structure of steel is in a supercooled austenite state and its hardness is considerably low as compared with that when it is in a martensite state. Therefore, it is conceivable that its machinability in this temperature region is naturally improved. A known example of working in this supercooled austenite state is ausforming (plastic working). Since it serves for the strengthening of steels, it has been substantially studied, both scholarlily and technically, and is increasingly used.